It is known in the automotive industry to join two metal preformed panels into a unitary hollow structural unit. Typical units of this type include vehicle doors, hoods, and trunk lids. Collectively, these units are referred to as closure panels.
A conventional process of joining the two panels together is referred to as hemming and results in a flange of the outer panel being folded over and gripping the edge of the inner panel. The process is well known. A conventional method and apparatus for joining two metal preformed panels is disclosed in U.S. Pat. No. 5,150,508 and its disclosure is incorporated herein by reference.
Conventional press style hemming machines require a tall press system having a base and platens on which upper and lower dies are mountable. The press system is actuated by a hydraulic cylinder having a limited stroke. Metal panels are nested together between the dies and the dies are moved toward each other to edge hem the two panels together. These conventional machines typically have a single hydraulic cylinder to drive the upper and lower dies, making it difficult to control pressing the corners of the panels together. Hydraulic fluid used in the hydraulic system is flammable.
These conventional hemming machines are costly and large requiring significant floor space and ceiling height. In addition, these machines require significant maintenance yet are difficult to maintain because of the limited stroke of the hydraulic cylinder which allows limited access between the upper and lower dies.